For the Cake 

1. Preheat your oven to 325 degrees Fahrenheit. Heavily spray a 10-inch bundt pan with cooking spray. This is essential for the bundt to come out cleanly.
2. In a medium bowl, whisk all purpose flour, baking powder, baking soda, and salt together until combined.
3. In a large bowl, whisk vegetable oil, granulated sugar, eggs, and sour cream together until smooth and fully combined.
4. Add about 1/3 of the dry ingredients to the large bowl of wet ingredients. Whisk until just combined. Add 1/2 of the buttermilk to large bowl and mix until fully incorporated. Repeat with another 1/3 of the dry ingredients, the remaining 1/2 of the buttermilk, and the final 1/3 of the dry ingredients. You will simply be alternating adding the dry ingredients and the buttermilk to the wet ingredients, starting and ending by adding the dry ingredients.
5. Transfer 1 1/2 cups (about 375g) of batter to a smaller bowl and another 1 1/2 cups (375g) of batter to another smaller bowl. Dye one of the smaller bowls red and the other blue. Add as much dye as necessary/desired.
6. Add 1/3 of the plain vanilla batter to your prepared pan. Add about 2 tablespoons (this does not need to be precise) of blue batter on top of the plain vanilla batter. Then, add 2 tablespoons (again, this does not need to be precise) of red batter directly on top of the blue batter. Finally, add another 2 tablespoons (once more, roughly 2 tablespoons) of the plain vanilla batter on top of where the blue and red batter meet. Repeat this process and work your way around the bundt, though feel free to have fun with adding the batter to create a unique design!
7. Tap the pan and slightly shake the pan before inserting it into the oven. Do not swirl with a knife or spoon.
8. Bake bundt for 40-50 minutes until a toothpick inserted into the center comes out with moist crumbs and the top springs back when poked with your finger. The top will be golden brown in color.
9. Let bundt cool for at least 45 minutes before carefully removing to finish cooling on a wire cooling rack!

For the Frosting

1. In a large bowl with a hand mixer or in the bowl of a stand mixer fitted with the paddle attachment, whip butter on high speed until smooth.
2. Add powdered sugar in 1/2 cup (30g) increments to avoid a mess, and mix until the frosting fully combines.
3. Add heavy whipping cream to the bowl. Whip on high speed for 5 minutes to create a light, fluffy, smooth, and whiter frosting.
4. Top cooled bundt with frosting as desired and decorate as desired.